1. Field of the Invention
The present invention relates to an antenna device and a mobile communication terminal, and in particular, to an antenna device for use in a radio frequency identification (RFID) system or the like and a mobile communication terminal that includes the antenna device.
2. Description of the Related Art
In recent years, an RFID system, in which predetermined information and electric power are transmitted and received by non-contact communication using an electromagnetic field between a reader-writer for generating an induction field and a wireless IC device that is attached to an object and that stores the predetermined information, such as an IC tag, has been developed as a management system for objects and information.
For example, Japanese Unexamined Patent Application Publication No. 2003-37861 discloses a cellular phone in which a non-contact IC card is embedded. However, a mobile communication terminal, such as a cellular phone, is small and multifunctional, so various metallic components are disposed in a small casing with high density. For example, a ground conductor and other elements are arranged on a plurality of layers on a printed wiring board that is to be a mother board, and components containing metal, such as IC chips and capacitors, are mounted on the surface of the printed wiring board with high density. In the casing, a battery pack that is to be a power source is also arranged, and the battery pack contains a metallic component, such as a frame.
Accordingly, there is an issue in that the communication performance of an antenna device disposed in a casing, such as an IC card, is affected by a metallic component in the casing. To ensure predetermined communication performance, it is necessary to increase the size of an antenna or reconsider the shape of the casing or the layout of the metallic component. However, such an approach is limited under the present circumstances.